Preparation Of Multifunctional Hydrogel And Its Application In Strain Sensors

Flexible sensor is an electronic device that senses changes in strain,pressure,gas,etc.,and can be used in the fields of human-machine interaction,health monitoring,and intelligent sensing.In recent years,soft materials such as hydrogels have outstanding performance in application of flexible sensors.Electronic hydrogel conductors using two-dimensional carbon materials as conductive media have limited applications due to poor transparency,poor biocompatibility,low flexibility,and low sensitivity under large strains.Ionic hydrogel conductors with conductive ions can achieve excellent properties such as transparency,high sensitivity,and large elongation.Moreover,an ionic hydrogel with self-healing and selfadhesive properties are more attractive to the preparation of flexible sensors.In this paper,two multi-functional hydrogels were prepared and their performance as flexible sensors was studied.(1)Mussel-inspired ionic hydrogel sensors consisting of sodium alginate(SA),tannic acid(TA)and acrylamide(AM)were designed and prepared.Based on the multiple weak Hbonds and synergistic interactions between the three components,the as-prepared hybrid hydrogel exhibits ultra-stretchability,high elasticity,good self-healing,biocompatibility,and high self-adhesiveness to diverse substrates both in air and underwater.More importantly,the ternary hydrogel exhibits an extremely large workable range of strain(0.05-2100%)and high strain sensitivity GF up to 9.Especially under subtle strains(<200%),the GF is 2.0,which is close to the theoretical value of the ionic hydrogel sensors.Besides,the sensor could work under an extremely low operating voltage down to 0.07 V.Consequently,the sensor demonstrates superior sensing performance for real-time monitoring of the large and subtle human motions,including limb motions,and wrist pulse.Therefore,it is believed that the STP hydrogel has great potential applications in health monitoring,smart wearable devices,and soft robots.(2)In order to fabricate a hydrogel that can achieve both excellent mechanical properties and good self-healing properties,a self-healing double-network hydrogel was prepared by a two-step process using SA,borate(Borax)and AM.This double-network hydrogel has good mechanical properties such as good transparency,high strength and toughness,and long elongation.It also has good self-healing properties due to the breaking and reconstruction of dynamic borate ester bonds in the system,which overcomes the difficulty of combing the mechanical properties and the self-healing properties.As a strain sensor,it can quickly and accurately monitor the movement of limbs and facial movements.As a pressure sensor,it can distinguish the heartbeat changes before and after human motions and vocal cord vibration,showing high sensitivity,rapid response and electrical stability.It is promising for the preparation of artificial skin and wearable smart devices for human health monitoring and disease diagnosis.